Substrate Addition Alters Carbon Dioxide and Methane Exchange in Incubation Experiments of Canadian Peatland Soils

Substrates added to peatland soils through anthropogenic disturbance alter carbon cycling and can shift these ecosystems from sinks to sources of atmospheric carbon. Isolating the direct influence these substrates have on peatland carbon cycling can be a challenge in field‐based studies due to interacting effects of vegetation and hydrometeorological shifts. Therefore, we performed a laboratory incubation study to understand the magnitude and duration of substrate addition impacts and their interaction with peat type and moisture content on carbon dioxide (CO 2 ) and methane (CH 4 ) exchange from peat under aerobic conditions. A total of 96 jars were incubated for 511 days in a full factorial study of four sites (two bogs, two fens), two moisture contents, and four substrate treatments (control, plant‐mix, mulch‐mix, road‐mix) with triplicate samples for each combination. Peat and substrate type significantly impacted CO 2 release and were dependent on their relative lability. Sphagnum peat had the lowest exponential decay constant at room temperature (0.040–0.094 yr −1 ), followed by softwood mulch (0.026–0.460 yr −1 ), fen peat (0.108–0.330 yr −1 ), and plant materials (0.161–0.429 yr −1 ). Road materials had a positive priming effect on peat decomposition, raising exponential decay constants by 1.4–4.5 times the control values. CH 4 exchange remained near zero across the experiment duration, with periods of detectable CH 4 uptake related to higher relative humidity. The observed carbon loss in response to substrate addition varied by site and moisture content, demonstrating the importance of constraining local conditions when understanding impacts on peatland decomposition processes as the result of anthropogenic disturbances.